Patent Document 1 discloses a laser projector for displaying an image on a projection surface by reflecting a laser beam emitted from a laser source from a scanning mirror so as to be projected onto this projection surface. The scanning mirror is freely displaced in the directions along two axes, and the mirror is oscillated with a resonance frequency particular to the mirror. In this laser projector, microscopic flickers, which are referred to as speckle noise, become a problem caused by the coherence particular to the laser beam. In order to reduce speckle noise, various techniques have been proposed, and as one of them, Patent Document 2 discloses a technique for using relaxation oscillations of the laser source. In this technique, a rectangular waveform pattern where on and off alternate is used to drive the laser source. The laser source starts relaxation oscillations at the time when off is switched to on, and the relaxation oscillations are maintained in the on period afterwards. This on period is set to be equal to or shorter than the time during which the relaxation oscillations converge. Accordingly, the output level of the laser source fluctuates unstably throughout the on period, and thus, the coherence of the laser beam lowers and the speckle noise is reduced.
In the laser scanning driven by the resonance frequency as in Patent Document 1, the speed at which the laser spot projected onto the projection surface moves in the scanning direction, that is to say, the scanning speed, is not constant, and the scanning speed is different depending on the image region on the projection surface. These characteristics of speed originate from the periodic fluctuations of the shifting angle per unit hour (angular speed) of the scanning mirror. The scanning mirror is driven by a drive current that corresponds to the resonance frequency, and the shifting angle thereof changes in a sine waveform along the time axis. The angular speed of the mirror is fastest when the shifting angle is minimum and slowest when the shifting angle is maximum. Accordingly, the scanning speed that links to the angular speed of the mirror is also fastest in the center area of the image that corresponds to the minimum shifting angle and slowest in the side areas (vicinity of the left and right ends) of the image that corresponds to the maximum shifting angle. Accordingly, the scanning speed that links to the angular speed of the mirror is fastest in the center area of the image that corresponds to the minimum shifting angle and slowest in the side areas (vicinity of left and right ends) of the image that correspond to the maximum shifting angle. Due to the difference in the scanning speed, the center area, which is scanned the fastest, tends to appear dark and the side areas, which are scanned the slowest, tend to appear bright even in the case where the same gradation is displayed. This is because the brightness perceived by the user depends on the integral value gained by integrating the strength of the output of the laser beam by time. In order to solve this inconsistency of brightness, Patent Document 3 discloses an image display device for enhancing the display brightness in the center area while lowering the display brightness in the side areas by correcting the driving signal for the laser diode, that is to say, the level of the current depending on the display location in the image.